plugin/k8s_extenral: Supports fallthrough option (#5959)
* Add fallthrough option to k8s_external plugin to allow transitioning control to the next plugin if the domain is not found * Exit on start up if required plugin is not present. Signed-off-by: vanceli <vanceli@tencent.com> --------- Signed-off-by: vanceli <vanceli@tencent.com> Co-authored-by: vanceli <vanceli@tencent.com>
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4 changed files with 66 additions and 22 deletions
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@ -10,8 +10,7 @@ This plugin allows an additional zone to resolve the external IP address(es) of
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service and headless services. This plugin is only useful if the *kubernetes* plugin is also loaded.
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The plugin uses an external zone to resolve in-cluster IP addresses. It only handles queries for A,
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AAAA, SRV, and PTR records; all others result in NODATA responses. To make it a proper DNS zone, it handles
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SOA and NS queries for the apex of the zone.
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AAAA, SRV, and PTR records; To make it a proper DNS zone, it handles SOA and NS queries for the apex of the zone.
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By default the apex of the zone will look like the following (assuming the zone used is `example.org`):
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@ -67,6 +66,14 @@ k8s_external [ZONE...] {
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* if there is a headless service with external IPs set, external IPs will be resolved
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If the queried domain does not exist, you can fall through to next plugin by adding the `fallthrough` option.
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~~~
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k8s_external [ZONE...] {
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fallthrough [ZONE...]
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}
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~~~
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## Examples
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Enable names under `example.org` to be resolved to in-cluster DNS addresses.
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@ -106,6 +113,18 @@ zone transfers. Notifies are not supported.
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}
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~~~
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With the `fallthrough` option, if the queried domain does not exist, it will be passed to the next plugin that matches the zone.
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~~~
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. {
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kubernetes cluster.local
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k8s_external example.org {
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fallthrough
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}
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forward . 8.8.8.8
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}
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~~~
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# See Also
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For some background see [resolve external IP address](https://github.com/kubernetes/dns/issues/242).
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@ -16,6 +16,7 @@ import (
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"github.com/coredns/coredns/plugin"
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"github.com/coredns/coredns/plugin/etcd/msg"
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"github.com/coredns/coredns/plugin/pkg/fall"
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"github.com/coredns/coredns/plugin/pkg/upstream"
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"github.com/coredns/coredns/request"
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@ -39,6 +40,7 @@ type Externaler interface {
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type External struct {
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Next plugin.Handler
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Zones []string
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Fall fall.F
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hostmaster string
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apex string
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@ -68,10 +70,6 @@ func (e *External) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Ms
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return plugin.NextOrFailure(e.Name(), e.Next, ctx, w, r)
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}
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if e.externalFunc == nil {
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return plugin.NextOrFailure(e.Name(), e.Next, ctx, w, r)
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}
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state.Zone = zone
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for _, z := range e.Zones {
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// TODO(miek): save this in the External struct.
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@ -93,6 +91,10 @@ func (e *External) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Ms
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m.Authoritative = true
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if len(svc) == 0 {
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if e.Fall.Through(state.Name()) && rcode == dns.RcodeNameError {
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return plugin.NextOrFailure(e.Name(), e.Next, ctx, w, r)
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}
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m.Rcode = rcode
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m.Ns = []dns.RR{e.soa(state)}
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w.WriteMsg(m)
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@ -1,6 +1,7 @@
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package external
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import (
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"errors"
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"strconv"
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"github.com/coredns/caddy"
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@ -9,7 +10,9 @@ import (
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"github.com/coredns/coredns/plugin/pkg/upstream"
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)
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func init() { plugin.Register("k8s_external", setup) }
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const pluginName = "k8s_external"
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func init() { plugin.Register(pluginName, setup) }
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func setup(c *caddy.Controller) error {
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e, err := parse(c)
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@ -21,14 +24,18 @@ func setup(c *caddy.Controller) error {
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c.OnStartup(func() error {
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m := dnsserver.GetConfig(c).Handler("kubernetes")
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if m == nil {
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return nil
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return plugin.Error(pluginName, errors.New("kubernetes plugin not loaded"))
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}
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if x, ok := m.(Externaler); ok {
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e.externalFunc = x.External
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e.externalAddrFunc = x.ExternalAddress
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e.externalServicesFunc = x.ExternalServices
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e.externalSerialFunc = x.ExternalSerial
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x, ok := m.(Externaler)
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if !ok {
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return plugin.Error(pluginName, errors.New("kubernetes plugin does not implement the Externaler interface"))
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}
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e.externalFunc = x.External
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e.externalAddrFunc = x.ExternalAddress
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e.externalServicesFunc = x.ExternalServices
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e.externalSerialFunc = x.ExternalSerial
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return nil
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})
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@ -70,6 +77,8 @@ func parse(c *caddy.Controller) (*External, error) {
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e.apex = args[0]
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case "headless":
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e.headless = true
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case "fallthrough":
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e.Fall.SetZonesFromArgs(c.RemainingArgs())
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default:
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return nil, c.Errf("unknown property '%s'", c.Val())
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}
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@ -4,24 +4,33 @@ import (
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"testing"
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"github.com/coredns/caddy"
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"github.com/coredns/coredns/plugin/pkg/fall"
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)
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func TestSetup(t *testing.T) {
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tests := []struct {
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input string
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shouldErr bool
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expectedZone string
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expectedApex string
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expectedHeadless bool
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input string
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shouldErr bool
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expectedZone string
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expectedApex string
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expectedHeadless bool
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expectedFallthrough fall.F
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}{
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{`k8s_external`, false, "", "dns", false},
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{`k8s_external example.org`, false, "example.org.", "dns", false},
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{`k8s_external`, false, "", "dns", false, fall.Zero},
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{`k8s_external example.org`, false, "example.org.", "dns", false, fall.Zero},
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{`k8s_external example.org {
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apex testdns
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}`, false, "example.org.", "testdns", false},
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}`, false, "example.org.", "testdns", false, fall.Zero},
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{`k8s_external example.org {
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headless
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}`, false, "example.org.", "dns", true},
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}`, false, "example.org.", "dns", true, fall.Zero},
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{`k8s_external example.org {
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fallthrough
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}`, false, "example.org.", "dns", false, fall.Root},
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{`k8s_external example.org {
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fallthrough ip6.arpa inaddr.arpa foo.com
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}`, false, "example.org.", "dns", false,
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fall.F{Zones: []string{"ip6.arpa.", "inaddr.arpa.", "foo.com."}}},
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}
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for i, test := range tests {
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@ -53,5 +62,10 @@ func TestSetup(t *testing.T) {
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t.Errorf("Test %d, expected headless %q for input %s, got: %v", i, test.expectedApex, test.input, e.headless)
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}
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}
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if !test.shouldErr {
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if !e.Fall.Equal(test.expectedFallthrough) {
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t.Errorf("Test %d, expected to be initialized with fallthrough %q for input %s, got: %v", i, test.expectedFallthrough, test.input, e.Fall)
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}
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}
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}
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}
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